The physical size of electronic systems has been the subject of a substantial development effort for a number of years. The space occupied by such systems has decreased markedly, as a result of a dramatic reduction in the size and power dissipation of the various components that make up the system. In particular, the large-scale integration of the circuitry of such systems has materially reduced the aggregate physical volume of the components of a system.
Even so, the "packaging" of these components in a minimum physical volume remains a challenge to the designers of these systems. As the volume decreases, one encounters increased difficulties and expenses in maintenance and repair due to the limited space and greater concentration of components within such systems. Further, the extraction of internally generated heat becomes more difficult, a significant problem in view of the temperature limits that must be maintained for reliable performance of the various components of such systems.
In general, groups of components which are functionally related are mounted on separate circuit boards. Thus, by choosing among a number of different boards, one may organize a system having the desired set of functional capabilities. The requirements of individual users are varied and a need has developed for "packaging" the circuit boards which permits the inclusion of different combinations of such circuit boards without materially degrading the heat extraction characteristics of the structure.